1. Field of the Invention
The present invention relates to a device for evaluating the quality of sleep.
2. Description of Related Art
Conventionally, a test called polysomnography (PSG) has been performed at hospitals to detect sleep stages. In a PSG test, brain waves (in an electroencephalogram, EEG), eye movements (in an electrooculogram, EOG), and chin movements (in an electromyogram, or an EMG of mentalis muscles) are recorded as parameters for detecting the sleep stages. This test, however, requires cumbersome operations because the electrodes must be attached on the body of the person being examined while measurements of the parameters are taken. Furthermore, specialized knowledge or skills are required for the operations of the measurement devices. Thus, the PSG test is not a test that can be readily performed at home.
On the other hand, in Japanese Patent Application Laid-Open Publication No. 2002-219116, there is disclosed a device for detecting, by providing vibration sensors such as piezoelectric elements under bedding, at least one of large movements (gross movements) and heart rate of a subject lying on the bedding, to compute the frequency of large movements or heart rate fluctuation based on the detected data and for determining sleep stages based on correlation between sleep cycles and the computed data. In Japanese Patent Application Laid-Open Publication No. 2006-280686, there is disclosed a device in which sleep stages are detected based on breathing activity so that the detection can be made more precisely.
The conventional devices, however, merely allow detection of the sleep stages, and it was not able to evaluate the degree of quality of sleep in a comprehensive manner.